Dive Cylinder Explodes - Sydney

[Diving Dubai]

@vincent54

So, a Hydro is carried out every 5 years, it measures the expansion of a tank under pressure. If the tank expands too much, bursts or fails to return to a dimension NEAR its original, then it's a fail. A hydro pressurises the tank to 40% above its working pressure

Hydro is only done every 5 years because it stretches the cylinder. The cylinder never returns to its original dimension.

Ideally you would hydro a tank yearly, but that would shorten its life, so there is a compromise, and in theory a defect not seen at one hydro wouldn't get critical by the next ( if the tank is being filled correctly - cave fills etc invalidate that assumption)

So VIP test. This is annually. The test should be able to find a defect before it becomes critical. Of course as I've said the Eddy current test is worthless and the visual inspection is open to interpretation and human error. I hope that helps.

Would I be worried about your tanks? From a professional stand point of black and white then yes. But the world is grey.

While I paint a black picture, the fact is that you can easily make a calulstion of tanks filled vs failures and come up with a tiny fraction of failures that is deemed to be acceptable.

Not great for the poor person in this incident. But we the consumer are guilty. If a person presents their tank for VIP and it fails, perhaps meaning they cancel a dive the majority would argue and demand a reinspection. Rather than accept the decision and buy a new tank.

My biggest concern is the home inspectors, those who have been on a course to pass their own tanks. It is those who potentiality have the least skills and are most prone to "overlooking defects"

 

[Rooster59]

This is nuts. Empty and drill holes in every one of these things. 1 person decides these tanks are ok to fill, and then exposes everyone within blast radius of your poor decision making. Let me guess, the person(s) injured are often not the person who decided the tank was ok to fill. Eddy testing isn't foolproof either.

 

[kelemvor]

@vincent54My biggest concern is the home inspectors, those who have been on a course to pass their own tanks. It is those who potentiality have the least skills and are most prone to "overlooking defects"

Not mine. Some dive shops, particularly larger ones, employ kids to fill tanks. Those kids have likely only got minimal instruction in how to do that part of their job. I'm sure it's not a given, but the "home inspectors" I've seen posting are inspecting and also filling at their home fill station. If they're also doing the fills, then they're taking on the risk of any deficiencies of their inspection. They have some incentive to do a good job. The kid salesman / part time tank inspector? He's got incentive to keep making the $1 over minimum wage he probably gets to keep inspecting tanks. That's not very much incentive to do a good job, hence why I would worry about his inspection.

In reading some of the papers that were shared on the subject of alu tank inspection - it sounds like it is kind of tricky to do it "right" to me. I'm glad to pay my dive shop (the one where the owner does the work himself) the $15 or whatever it is for a VIP. I hope he does it right, but since I don't know how to do it right, how can I credibly critique him? I'm glad I dive mostly steel tanks.

I've definitely learned a lot today. Before this thread and the linked articles, I thought inspecting (and performing eddy current tests) were straightforward and easy. Obviously not.

 

[Shotmaster]

My personal opinion is that there should be a more aggressive plan to remove these cylinders from service. When you consider that they have been in service between 20-45 years, and their value in the market place is at or barely above the scrap value (from my experience I see old Dacor and U.S. divers tanks listed for $30-60 regularly) and newer used aluminum selling for $80-120, I don't see the risk/reward value for the dive industry trying to get maximum service life from them. I do understand the larger commercial gas supplier industry with some 25 million cylinders in service worldwide having an issue with this, but then again, when one lets go, it won't be one of the business tycoons standing next to it, it will be some poor worker and just another short lived news headline.

 

[clownfishsydney]

My information is, that if this was one of the 6351 (typo corrected) cylinders, then Workcover NSW (OH&S investigators and enforcers) will be putting a total ban on the filling of them by commercial operators in New South Wales. I would then expect that all the other states of Australia would also institute a similar ban.

 

[akdeepdiver]

So..I'm confused, no SCUBA cylinders I know of have been made of "6051" alloy. Are you mistaking it for 6351 alloy or 6061 alloy?

 

[Centrals]

@vincent54



Hydro is only done every 5 years because it stretches the cylinder. The cylinder never returns to its original dimension.

I have been told that hydro testing on scuba tank is required every year in Australia. Could anyone verify it please?

 

[davegster]

Taken from Cylinder Testing - The Scuba Doctor :

In Australia all scuba cylinders are required to be hydrostatically tested every twelve months.

This is carried out in accordance with Australian Standard 2030.1 by a Certified Test Station.

The cylinder is then stamped around the neck area indicating the month and year it was tested along with the test station number.

Aluminium cylinders manufactured from 6351 aluminium are required to have an ultrasonic or eddy current neck test every two years to inspect for neck cracks that may have developed over time relating to that grade of aluminium. This is indicated with E stamped as part of the test stamp. It is sometimes called a "Visual Plus" test after the instrument used to conduct the test.

If the cylinder does not have a current test stamp, it will not, and should not, be filled.

 

[Hemrick]

Before I ask this let me put out that I don't speak with any authority, purely using this discussion from knowledge people who may have some knowledge of the issue to ask a question.


Australian Standards requires a hydro every 12 months, according to my wikipedia research the next closest country interval wise is Norway at 24 months while most other countries are at the 3-5 year mark.


Talking to someone in the US who has been in the scuba industry a long time I have been told that after a hydro it takes the scuba tank about 2 years to return to its original size (this is the hearsay bit don't shoot the messenger, I'm just after a discussion). If this was the case a 12 month hydro will never let the cylinder return to its original size, it also results in between 2 and 5 as many stamps on the shoulder of the tank as in other place. Even if the stamp itself doesn't do anything to the cylinder on a steel tank it breaks down the paint and can open the door to surface rust.



So finally to my question, is every 12 months excessive for a hydro? What do manufactures recommend for their tanks and way does Australia feel the need to be so different from the rest of the world?


(P.S I haven't actually read to Australian Standard, I tried to but don't feel like paying $300 to read a standard)

 

[clownfishsydney]

I was part of a committee that set the Australian Standard, but my spot on it was replaced before it actually was adopted. The committee was dominated by people who had a vested interest in having pressure tests done as often as possible. That is, dive shop owners, testing stations etc. It was inevitable that this would be the outcome.

As I fill my own cylinders, I only get them tested every three years or so. I make sure that I have at least a few cylinders in test in case we travel somewhere and need to get a refill.

PS I have corrected the typo in my previous post about the alloy type.